Two words are becoming very familiar with in many American schools: Common Core. The new national education program brings new testing and new standards to classrooms. The rollout has begun across the country, but a growing number of educators are expressing discomfort. Many worry that the effort is being rushed, and that people are not focusing enough on the potential impact. After all, they point out, Common Core won't just be gauging student's progress. It will also evaluate teachers, rate schools and rank states.

NPR's Claudio Sanchez reports that this growing unease could delay or even derail implementation.

CLAUDIO SANCHEZ, BYLINE: Olathe East High School in Olathe, Kansas is holding one of its parent-teacher conferences today. The turnout is good. There are grades and behavior issues to discuss, questions about courses and college options.

Not a peep, though, about the Common Core standards and new tests in Math and English, Language Arts, arguably one of the biggest changes in what schools in Kansas and across the nation will teach and test. It's just not on parents' minds. Besides, says Principal Bill Weber, even educators can't fully explain what's ahead. It's like driving in a fog.

BILL WEBER: It's definitely a fog. You know, in the state of Kansas, yes, we have adopted the Common Core, but we still do not know what the assessment will be that we're going to be administering to kids. And so we're in a lot of unknowns in terms of what is going to happen, and so that's ultimately a struggle that we face.

SANCHEZ: Kansas is one of 45 states that adopted the Common Core, in part because the Obama administration gave millions of dollars to states that adopted college and career-ready standards implicit in the Common Core.

But Kansas is also one of eight states that have pulled out of the two organizations that are developing tougher tests that'll be aligned with the new standards.

It's been a hard sell, because of a growing concern that these tests will drive the curriculum, what teachers teach, denying local educators any say in the matter. Olathe schools superintendent Marlin Berry says that concern is overblown.

MARLIN BERRY: We've not lost any local control in terms of what's going to be taught in our classrooms. We have had this conversation at multiple board meetings, and we think there's some benefits. So now a fourth grader in North Carolina is going to learn about the same thing - or they should - as a fourth grader in Kansas.

SANCHEZ: Supporters of the Common Core say that's the whole point, that students across the nation be taught and tested based on the same academic standards, not 50 different versions. Rick Hess, of the American Enterprise Institute, says the problem is that Common Core proponents went forward without really explaining all this.

RICK HESS: Suddenly, you're both piloting the assessments before anybody knows what they are, and attaching consequences, and you're seeing huge pushback from some teachers who are saying, wait a minute. This is not at all what we thought we were signing up for.

SANCHEZ: The impatience of Common Core proponents, Hess argues, has turned out to be a huge mistake. And because the public's understanding was so shallow...

HESS: It inherited a lot of the animus that's been directed towards No Child Left Behind standards and testing.

SANCHEZ: No Child Left Behind, after all, started what some call a tsunami of standardized testing that angered and mobilized parents and teachers who now see the tests aligned to the Common Core as more of the same: a test-driven reform that stresses kids out and robs them of a well-rounded education.

DR. ELEASE FREDERIC: You teach, you test. You re-teach, you test.

SANCHEZ: Dr. Elease Frederic, schools superintendent in Halifax County, North Carolina, says the focus on testing is excessive, given all the other things school districts have to do to prepare for the Common Core.

FREDERIC: And it's going to take time. We just started lots of new things in North Carolina with Common Core, with assessments, with this, with that. People are kind of oomph, what next? We can't anymore.

SANCHEZ: Testing experts say if you're going to test students based on the new standards, you first have to give states time to develop new curricula so that kids have a chance to learn the new, more rigorous content.

Then you have to give teachers the training necessary to make the switch from what they've been teaching and how they've been teaching. And you have to do it all before you hold anybody accountable for how they do.

So why have the Common Core standards and tests been so rushed? Proponents know there's a very narrow window of time for everything to come together before it gets bogged down in political and ideological squabbles.

ROBERT BRENNAN: That window isn't going to stay open forever.

SANCHEZ: Robert Brennan, of the University of Iowa, is advising the people who are designing the new tests. He says despite all the confusion and angst, Americans will eventually see the value of the Common Core.

BRENNAN: I do think there's enough buy-in by states that I'm fairly optimistic that they are going to result in improved testing of a type that will give us a better understanding of the depth of knowledge our children have or don't have.

SANCHEZ: Brennan predicts that no matter how many more states defect from the Common Core, they can't go back to the kind of weak academic standards and tests that have made it so hard to figure out what American students really know and are able to do. Claudio Sanchez, NPR News. Transcript provided by NPR, Copyright NPR.